Clinical biochemistry: haemoglobin variants: practice question

A Biochemistry question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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Biochemistry · Clinical biochemistry: haemoglobin variants

Sample item

A 22-year-old woman has mild anaemia with haemoglobin 10.5 g/dL, MCV 62 fL, red cell count 5.6 million per microlitre and a normal serum ferritin. Which investigation is most likely to confirm the diagnosis?

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

D. HPLC showing raised HbA2

Marked microcytosis with a high red cell count and normal ferritin, giving a Mentzer index (MCV/RBC) of 62/5.6, about 11, below 13, suggests beta-thalassaemia trait. Reduced beta-chain output raises the proportion of HbA2 (alpha2delta2) to above about 3.5%, which HPLC or electrophoresis detects. Iron therapy is not required in the absence of iron deficiency.

Option by option

  • A. Bone marrow iron stain

    A marrow iron stain would be used when iron status is uncertain, which ferritin already clarifies.

  • B. Sickling test

    A sickling test detects HbS, which does not cause this microcytic picture.

  • C. Serum transferrin saturation

    Transferrin saturation is low in iron deficiency, which a normal ferritin makes unlikely.

  • D. HPLC showing raised HbA2 (correct)

    Correct. Raised HbA2 is the diagnostic feature of beta-thalassaemia trait.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

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Questions about this Biochemistry question

What is the answer to this Biochemistry question?

The best answer is D, HPLC showing raised HbA2. Marked microcytosis with a high red cell count and normal ferritin, giving a Mentzer index (MCV/RBC) of 62/5.

Why is "Bone marrow iron stain" not the answer?

A marrow iron stain would be used when iron status is uncertain, which ferritin already clarifies.

Why is "Sickling test" not the answer?

A sickling test detects HbS, which does not cause this microcytic picture.

Why is "Serum transferrin saturation" not the answer?

Transferrin saturation is low in iron deficiency, which a normal ferritin makes unlikely.

What concept does this question test?

It tests Clinical biochemistry: haemoglobin variants in Biochemistry. 6, about 11, below 13, suggests beta-thalassaemia trait. Reduced beta-chain output raises the proportion of HbA2 (alpha2delta2) to above about 3.5%, which HPLC or electrophoresis detects. Iron therapy is not required in the absence of iron deficiency.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Clinical biochemistry: haemoglobin variants?

Build one table of enzyme deficiency, disease, inheritance and key finding, then revise it by spaced recall. Then use the flashcards and the other Biochemistry questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.